In long-term sight is it more profitable to let your planets population grow.
But the growth hangs from the taxes you set. Low taxes increase the growing and no taxes far more, but the higher taxes you set, the lesser population growth you get. At 10% you getting no more growth and all over 10 will indeed decrease your population.
Should be clear to every one that investing in the growth of the planets is a investation for future tax incomes. More People = more people who pay taxes